This invention relates to a foundation piling system, and more particularly to such a system which enjoys improvements over conventional foundation supports for houses, buildings and the like.
In home and building construction, exterior grade beams, or footings, are often utilized which are formed in ditches, or the like, to support the exterior walls of the building. These concrete grade beams are often poured in conjunction with a continuous slab which extends in the area between the grade beams and can be poured simultaneously with, or separate from, the grade beams.
However, problems are encountered in connection with these type arrangements, especially when the building site contains soil of varying compactness and plasticity. For example, in cases when a building site is extensively graded to level it and soil is moved from one portion of the lot to the other, the soil immediately underneath the removed soil is relatively compact while the soil that is moved to other portions of the building site is relatively loose. This, of course, causes differential movements of the foundation and the grade beams and potential problems with regard to cracking, breaking, or the like.
Several techniques have been suggested to combat these problems. For example, a concrete pier system has been suggested in which relatively deep holes are formed and concrete poured into the holes to form a pier for the exterior grade beam. However, these concrete piers have several disadvantages. For example, the depth to which the beam is formed is often based on a single soil test at one area which is not necessarily representative of the entire area. Thus the pier, although adequate in height for the particular area tested, may be insufficient to adequately support the foundation in other areas having a softer or more plastic soil composition.
Also, the drills used to drill the pier holes do not necessarily clean out the bottom of the holes which causes difficulty in the stability of the beam once it has been poured. Further, the pier drill may encounter soft rock strata or the like which jams the drill and causes undue delays. Still further, upheaval forces, i.e., forces in the upward direction often occur due to the changes in the wetness or the dryness of the soil which causes a poured concrete pier to fail. Still further, in soils having a large percentage of clay there is a certain practical limit on the height of the pier, which does not necessarily support the foundation adequately in this type of environment.
Other techniques for constructing an adequate exterior grade beam support include a post tension technique in which cables are passed through the forms for the grade beams and, after the concrete is poured thereover, are placed in very high tensile stress to increase the resistance of the foundation to cracking or failing. However, these types of techniques require a great deal of labor and are also subject to fail.